An alternative to surgically removing unwanted biological tissue (e.g., malignant tumors, infected tissue, etc.) from a patient is to use thermal treatment to destroy the unwanted tissue. Such thermal treatment is a process of heating up or cooling down (i.e., thermally ablating) biological tissue in order to destroy the cells of the tissue. Additional information with respect to thermal ablation can be found in U.S. Pat. No. 6,542,767 issued to McNichols et al. on Apr. 1, 2003 which is incorporated by reference herein in its entirety.
Interventional image-guided ablation therapies using thermal energy sources such as radio frequency (RF), microwave, laser, high-intensity focused ultrasound (HIFU), and cryogenics have received much recent attention as minimally invasive strategies to cure cancer. Additional information with respect to image-guided ablation therapies using thermal energy sources can be found in U.S. Pat. No. 6,542,767 issued to McNichols et al. on Apr. 1, 2003 which is incorporated by reference herein in its entirety. Potential benefits of such techniques include the ability for near real-time image guidance using magnetic resonance (MR), x-ray computed tomography (CT), or ultrasound, the ability to ablate cancerous tumor in non-surgical candidates, and the potential to perform the procedure on an out-patient basis. Further, it is believed that image-guided ablation therapy may eventually compete with some open tumor surgeries. The successful application of interventional technology to minimally invasive treatment of localized pathologies has the potential to prolong life while reducing the morbidity and cost associated with a more invasive surgical approach.
Typically, a medical doctor (i.e., the user of a thermal treatment tool) will perform the thermal treatment and then later have a medical image of the treated physiological region created to evaluate the success of the treatment. Such a post-treatment evaluation does not allow the doctor to determine, in real-time, if he has successfully destroyed all of the unwanted biological tissue, or if he has inadvertently damaged healthy tissue. Also, post-ablation structural images may not distinguish the edema that surrounds the thermal lesion from tumors, hemorrhage, or prior inflammation.
Methods of image-guided thermal treatment have been developed which use imaging thermometry techniques in conjunction with a cell-death model to allow a user to monitor the effects of the thermal treatment in real or near-real time. However, these cell-death models, used to date, are typically not very robust. The cell-death models often under-estimate or over-estimate the effects of the thermal treatment. Also, a cell-death model which is adequate for treating one type of tissue may not be effective in treating another type of tissue. Additional information with respect to medical thermometry can be found in U.S. Pat. No. 6,542,767 issued to McNichols et al. on Apr. 1, 2003 which is incorporated by reference herein in its entirety.
Some models assume that the tissue response is independent of temperature history. Others use a mathematical model of the temperature-time relationship for tissue damage. Such models usually consist of either a generalized Arrhenius function or a linear approximation of the Arrhenius function near 43° C. However, these models and parameters are based on experiments at lower temperatures and significantly longer heating durations than typical for clinical ablations. Previous studies have shown that the empirically-derived parameters used for these Arrhenius-based models can vary for different tissues, temperature ranges, and heating durations.
A time-temperature product model was not successful, and a critical temperature model which did not account for heating duration did not work very well and was sensitive to transient noise in the temperature data.
Therefore, it is desirable to develop and implement a robust cell-death model which accurately predicts the effects of thermal treatment on many different types of biological tissue.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with the present invention as set forth in the remainder of the present application with reference to the drawings.